Platelet-activating factor (PAF) is a lipid mediator that may be involved in the development of airway inflammation. PAF may be produced by inflammatory cells and by airway epithelial cells. PAF in the airway may serve as a chemoattractant, induce eicosanoid production, cause airway mucus secretion and cause bronchospasm. A technique developed by others has been used to assay PAF in bronchial lavage fluid before and after transbronchoscopic challenge. Bronchial lavage fluid is added to ethanol with deuterated PAF and lyso-PAF internal standards, extracted on a reverse phase column and silicic acid solid phase columns, derivitized with pentafluorobenzoyl chloride, and assayed on a gas chromatograph with an negative ion chemical ionization mass ion detector. Two transbronchoscopic bronchial challenge protocols are currently in progress. They involve the endobronchial instillation of endotoxin to normal volunteers in one protocol with repeat bronchoscopy at 2, 6, or 24 hours. In the second protocol, endobronchial instillation of antigen to allergic asthmatic patients is followed by a repeat bronchoscopy 24 hours after antigen instillation. In both protocols, bronchial lavage PAF levels are being measured. Bronchial lavage PAF is measurable in the range of 5 to 150 pg/ml bronchoalveolar lavage. Both studies are continuing to accrue patients. These studies may provide additional information on PAF production in the setting of acute airway inflammation.